This invention relates to a novel aromatic polyester, a novel aromatic polyesteramide, and compositions thereof.
In these years, there is an increasing need for polymeric materials having not only excellent mechanical properties such as tensile strength and modulus, but also excellent heat resistance and chemical resistance. One type of polymeric material satisfying such a requirement is a class of liquid crystalline polyester and polyesteramide which is easy to polymerize and mold and has excellent mechanical properties because of molecule orientation.
All aromatic polyesters are widely known as liquid crystalline polyesters. For example, homopolymers and copolymers of p-hydroxybenzoic acid have been commercially produced and marketed. Some of these all aromatic polyesters, however, cannot be melt molded because their melting point is too high, and others are difficult to mold because their melt viscosity is high.
It was proposed to produce aromatic polyesters having a lower melting point by copolymerizing various components with p-hydroxybenzoic acid. Examples of prior art p-hydroxybenzoic acid copolymers are listed below by referring to the patents disclosing them.
(1) Japanese Patent Application Kokai No. 54-139698
Copolymers of p-hydroxybenzoic acid with isophthalic acid and hydroquinone have a higher melting point.
(2) U.S. Pat. No. 3,637,595
Copolymers of p-hydroxybenzoic acid with terephthalic acid, isophthalic acid, and an aromatic dihydroxy compound such as hydroquinone are highly heat resistant and provide a molded article having high strength. But the melt molding temperature is extremely high.
(3) U.S. Pat. No. 4,067,852
Aromatic polyesters are prepared by copolymerizing p-hydroxybenzoic acid, 2,6-naphthalene dicarboxylic acid, and an aromatic dihydroxy compound.
(4) U.S. Pat. No. 4,169,933 (Japanese Patent Application Kokai No. 54-30290)
Aromatic polyesters are prepared by copolymerizing p-hydroxybenzoic acid, 2,6-naphthalene dicarboxylic acid, terephthalic acid, and hydroquinone.
(5) U.S. Pat. No. 4,083,829
Aromatic polyesters are prepared by copolymerizing p-hydroxybenzoic acid, 2,6-naphthalene dicarboxylic acid, isophthalic acid or resorcin, and an aromatic dihydroxy compound.
(6) U.S. Pat. No. 4,130,545
Aromatic polyesters are prepared by copolymerizing p-hydroxybenzoic acid, 2,6-naphthalene dicarboxylic acid, m-hydroxybenzoic acid, and an aromatic dihydroxy compound.
These aromatic polyesters (3) through (6) have a relatively low melting point so that they are melt moldable. Some polyesters are said to be spun into a filament having a strength of the order of 6 to 10 grams/denier. These polyesters suffer from a relatively low heat distortion temperature.
Among aromatic copolyesters available in the prior art, certain copolymers are heat resistant, but cannot be molded or can be molded with difficulty because the heat resistance is accompanied with a high melting or flow temperature. Some copolymers are difficult to mold because the melt viscosity is increased despite the degree of polymerization of copolyesters. Some other copolymers contain infusible particulates after polymerization and suffer from poor moldability. Conversely, those copolymers characterized by good moldability because of a low melting or flow temperature are not fully heat resistant.
Although the melting temperature of a resin is desired to be lower for ease of molding, a resin having a lower melting temperature exhibits lower heat resistance too. Ideally speaking, a resin is desired to have as high a heat resistance and as low a melting temperature as possible.
Liquid crystalline polyesteramides are modified polyesters in which amide bonds are incorporated in addition to ester bonds for the purpose of improving the adhesion, fatigue resistance and anisotropy of liquid crystalline polyesters. They are disclosed in a number of patents, for example, Japanese Patent Application Kokai Nos.
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Liquid crystalline polyesteramides do not have a marked drawback as described below which is common in liquid crystalline polyesters.
Liquid crystalline polyester has the nature known as anisotropy that the strength of a melt molded resin in a machine or oriented direction (MD) is substantially different from that in a transverse direction (TD). Since rupture of an injection molded part by an external force generally takes place at the weakest site, cracks occur in a molded part of liquid crystalline polyester in its transverse direction (TD). To improve the practical strength of liquid crystalline polyester, the anisotropy thereof must be mitigated, that is, the TD strength thereof must be increased.
As to aromatic polyesters, they have drawbacks common to liquid crystalline polyesters as previously described. More particularly, aromatic polyesters exhibit outstanding anisotropy with respect to mechanical strength, coefficient of linear expansion, and mold shrinkage factor and tend to be marred on the surface. Improvements in these points are desired. A new approach for eliminating the anisotropy and marring of aromatic polyesters is also desired.
Plastic magnets or magnetic resin compositions are inferior in magnetic characteristics to sintered magnets, but have the advantages that a number of products can be readily obtained by injection molding, and they are lightweight and can have a complicated shape. Plastic magnets include magnetic powder and binder resins which are usually epoxy resins and polyamide resins such as nylon-6 and nylon-66. Therefore, the mechanical strength and heat resistance of plastic magnets depend on the particular type of resin used as the binder. For example, plastic magnets based on heat resistant epoxy resins have a heat distortion temperature of from 100.degree. to 120.degree. C. and magnets based on nylon have a heat distortion temperature of from 140.degree. to 160.degree. C.
In order that magnetic resin compositions may find a wider variety of applications, it is important to increase the heat resistance of the compositions. In general, a composition comprising a more heat resistant resin are more difficult to mold, losing the advantage of magnetic resin compositions that a number of parats can be obtained and can have a complicated shape.
It is also desired that magnetic resin compositions having high moldability and heat resistance be mitigated in anisotropy and improved in mechanical strength.